Dot 5 Silicone Brake Fluid

[Stev0]

I replaced my old fluid with Dot 5 Silicone Brake fluid today without really doing any research. Rumors have it that it will be very hard on the rubbers.


Should I change it to 5.1 or leave it as is?

 

[Theo]

According to Wikipedia, it's a silicone-based fluid, while DOT 4, 3 and 5.1 are polyglycol ether based fluids:
http://en.wikipedia.org/wiki/DOT_5
http://en.wikipedia.org/wiki/DOT_4
A not professional racer told me that a DOT 5 should not be used in DOT 4 brake systems.

 

[Stev0]

Shoot, ill change it tomorrow. thanks

 

[268fords]

Old local racer told me about this stuff. My brakes used to howl as they heated up and I used to wonder what all the hype was about brembo brakes. Changed to maxima high temp fluid and have a new found love for my brakes. Downhills that used to cook my brakes and leave me with nothing had not one bit of an effect on my brakes.

 

[Tinken]

We use Motorex 5.1 brake fluid. I changed out my oem 4.0 due to that spongy feeling and my brakes are solid.

 

[Norman Foley]

I use 5.1 in place of 4.0 fluid. Motul or Motorex. 5.0 silicone is not compatible with others.

 

[R_Little]

Not supposed to mix them.

DOT 5 is for long term storage as it does not absorb water.

I put DOT 5 in my Studebaker 20 yrs ago.

it is still clean as a whistle...DOT 4 would be black by now.

 

[Xcuvator]

We use Motorex 5.1 brake fluid. I changed out my oem 4.0 due to that spongy feeling and my brakes are solid.

So you are sure it was the fluid type and not some sneaky air? If so I will flush and try it.

 

[Tinken]

So you are sure it was the fluid type and not some sneaky air? If so I will flush and try it.

Haha, yes, sure. I just swapped the DOT 4 for 5.1 in Stacy's race bike on Friday. Course her's was brown and jelly , but they came out hard as a rock when finished.

 

[Xcuvator]

Haha, yes, sure. I just swapped the DOT 4 for 5.1 in Stacy's race bike on Friday. Course her's was brown and jelly , but they came out hard as a rock when finished.

Sounds good.I would like to start switching the bikes over. I wonder how critical it is to get every trace of the DOT4 out? In other words will they mix well together? Since they are both polyglycol either based, I would think so..

 

[Tinken]

Yea, I sucked it out with a syringe, not really worried about getting it all out.

 

[CJBROWN]

Wow and holy smokes...so much disinformation here.

First of all, 5.0 silicone fluid is NOT what you want for a standard braking system. Flush it out and install 4.0.

5.0 and 5.1 is for a race track, they have a higher boiling point and helps race cars prevent caliper boil and brake loss. There is zero benefit on a motorcycle, well maybe a road racer. The big downside is the higher the dot rating the more it absorbs moisture which makes fluid boil earlier. So you could actually experience brake failure with a 5.1 for failure to change it out when it collects too much water.5.0 is the silicone synthetic and is not compatible with the seals in your dot-4 system.

What's the matter with using Dot 4 - what the manufacturer recommends????

Oh, and the spongy brakes - the fix had nothing to do with the dot rating - you just got the air in the line purged out, that's why your brakes firmed up.

You guys are over-thinking this. Just change out with dot 4 once a year - draw out the reservoir and replace, bleed out at the caliper nipples, replace with fresh fluid in the reservoir. Easy-peasy.

Here's a post from a euro-car enthusiast forum on changing out 5.0 for 3 or 4:

You're not going to like this.. Solvent will need to be used to flush out the entire brake system. This also means taking all the hydraulic cylinders apart (yes, brake, clutch masters, brake calipers, clutch slave cylinder apart and flush clean them along with the hoses) to get all that DOT 5 out. Stuff will not bleed out with new brake fluid.

One nasty thing about silicone, it tends to stick and does not come off easy. Cars that are painted with any trace of silicone will result in spots where the silicone once was.

IMO, no one should use DOT 5 brake fluid in any car. DOT 5 was invented for military vehicles that are subjected to harsh/humid conditions where DOT 3 brake fluid would cause system corrosion problems due to harsh conditions and extremely extended service intervals.

Reasons why some are lead to use DOT5, it does not harm paint, last longer (so what, brake fluid should be changed yearly, if the car is driven on a track day, it should be flushed after the track event). Those two reasons are simply not logical and rational justification to use DOT5.​

 

[Tinken]

Wow and holy smokes...so much disinformation here.

Sorry Brown, I found your whole post some what confusing. Although there are some really good points that you made.

What's the matter with using Dot 4 - what the manufacturer recommends????

Actually Husqvarna recommends either Dot 4 or Dot 5.1. Dot 5 should not be used.

There is zero benefit on a motorcycle, well maybe a road racer. The big downside is the higher the dot rating the more it absorbs moisture which makes fluid boil earlier. So you could actually experience brake failure with a 5.1 for failure to change it out when it collects too much water.

This statement is misleading. Dot 5.1 is fractionally more hygroscopic than Dot 4, but 5.1 maintains a higher boiling point when wet. Therefore when comparing wet 4.0 with 5.1, the 4.0 will fail long before the 5.1 will.


Both Dot 4 and Dot 5.1 are Polyalkylene Glycol Ether. Both of these fluids are hygroscopic, meaning that they will absorb water, but they can and still perform adequately. However water will reduce their boiling points. Poly Glycol fluids are two times less compressible than silicon based fluids (Dot 5.0). Dot 5.0 should not be used.

The table below shows both wet and dry boiling points. The first temperature is the dry boiling point which indicates a moisture free system. The second is a wet system or a system that has absorbed water and has not been flushed. As you can see between Dot 4.0 and Dot 5.1, the 5.1 has a higher boiling temperature, especially when it has had moisture introduced.

DOT 3__________401ºF__________284º __________ Compatible

DOT 4__________446º F__________311º F_________ Compatible

DOT 5__________500º F__________356º F_________ Not Compatible

DOT 5.1________518º F__________375º F_________ Compatible

• Dot 5.1 is fractionally more hygroscopic than Dot 4, but 5.1 maintains a higher boiling point when wet.
• Most people will never boil your brake fluids on their motorcycles.
• Everyone should change out their brake fluid annually.
• Dot 4 and 5.1 are priced similarly, so buying 5.1 makes perfect sense.

So why even still sell Dot 4? Some claim that Dot 4.0 should be used in cars which will likely not have their fluids serviced annually. This is simply nothing more than a myth since Dot 5.1 maintains better functionality, even when wet.

 

[CJBROWN]

Boiling point is irrelevant on a dirtbike. Dot4 is sufficient.

You gave a very elaborate dissertation to say 5.1 has a slightly higher wet boiling point - conceded.

The important thing for the OP is to get the silicone fluid out of there, right?

 

[BobPS]

(snip) The important thing for the OP is to get the silicone fluid out of there, right?

That's right. Flush the brake.
I would suggest getting a MityVac to make brake bleeding that much easier.

My TE 630 has only about 200 km but the rear brake fluid was already black. I don't know what the original brake fluid is... I just changed the rear brake fluid of my TE630 with a Motul dot 5.1 brake fluid. Haven't changed the front brake fluid, cause I don't have enough fluid to flush the brake.

Motul 5.1 is the brake fluid I use on my Monster's brakes and also in the Monster's hydraulic clutch... If only the hydraulic clutch on my TE 630 could use the same brake fluid, it would make life much simpler